This invention relates to an internal pressure adjustable bed which is concerned with the art of internal pressure adjustment for beds and which belongs to the bed of International Patent Classification A47C.
Generally in many beds, the internal pressure of a mattress mounted thereon, namely the hardness of the mattress surface, is uniform throughout the surface. However, a human body lying on the mattress gives different loads in the head, breast, hip and leg, so if the internal stress of all portions of the mattress is constant, there occur differences in the depression amount among such portions of the human body. To give a proper amount of elasticity to the mattress surface to thereby improve comfortableness, a large number of coiled springs are mounted upright and close together between the upper and the lower face of the mattress, or an elastic material such as a foamed synthetic resin is interposed therebetween. However, this is disadvantageous in that a human body lying on the mattress is depressed in the form of V letter because usually the hip gives the largest load. Thus, in conventional beds it has been impossible to obtain such a sleeping posture as is considered desirable from the standpoint of health. In an attempt to remedy this drawback there has been proposed a method in which springs or elastic materials are interposed between the upper and the lower face of a mattress so as to be different in internal stress beforehand in various positions, and the elastic modulus of average positions on which large loads are placed is made large. In another method proposed, springs or elastic materials which are homogeneous or same are mounted within a mattress and the lower face of such springs or elastic materials is supported by a pre-curved bottom plate, so that the amount of displacement of the springs or elastic materials is changed and the internal stress changed to the direction of the plane of the mattress.
In such a fixed typed bed, a human body, if it matches a designed physical constitution, will of course be borne horizontally on the bed, but when a person whose physical constitution is different from an average physical constitution, e.g. a child, uses the bed, his feeling in bed will become worse because of inequality in hardness of the mattress surface, and thus it is impossible for users with different physical constitutions to always enjoy a good feeling of use. Beds of this sort are further disadvantageous in that, when they are used for many years, springs or elastic materials will deteriorate resulting in depression of the mattress surface, and that usually such deterioration occurs biasedly with respect to the mattress surface. Means for its correction has not been available, so a bed which eliminates all of the above drawbacks has been desired.